Track preschool planning days, partner invites and real vacation forfeiture

Three strands of work that grew together across the same settings screen and
API client, so they land as one change.

Per-year preschool planning days ("studiedagar"): new table, repository
(SQLite + Postgres), service, router and migration 007, plus the hooks and
Settings UI to plan and record them per child and year. Allocation now
reserves the recorded figure for a year where one exists and only falls back
to the child-level estimate otherwise, marking that fallback as assumed.

Partner invitations: workspaces issue and list invitations, registration
accepts an invite token to join the inviter's workspace instead of creating a
personal one, and a /join/:token page plus the settings invite panel drive it.

Vacation forfeiture: tips and the dashboard now distinguish days a parent
genuinely loses from days that merely age, so the warning stops firing on
balances that were never at risk.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/tests/unit/test_preschool_planning_days_router.py

@@ -0,0 +1,88 @@
+"""API-level tests for `/api/preschool-planning-days`.
+
+Uses the shared `authed_client`/`seeded_ids` fixtures (see `tests/conftest.py`)
+since these routes are scoped per child within the caller's own workspace.
+"""
+
+from uuid import uuid4
+
+from httpx import AsyncClient
+
+from tests.conftest import SeededIds
+
+
+class TestPreschoolPlanningDaysRouter:
+    async def test_get_year_with_no_row_returns_child_default(
+        self, authed_client: AsyncClient, seeded_ids: SeededIds
+    ) -> None:
+        resp = await authed_client.get(f"/api/preschool-planning-days/{seeded_ids.child_id}/2026")
+        assert resp.status_code == 200
+        body = resp.json()
+        assert body["is_default"] is True
+        assert body["id"] is None
+        assert body["planned_days"] == 6  # Child entity default
+        assert body["taken_days"] is None
+
+    async def test_upsert_planned_then_record_taken(
+        self, authed_client: AsyncClient, seeded_ids: SeededIds
+    ) -> None:
+        put_planned = await authed_client.put(
+            f"/api/preschool-planning-days/{seeded_ids.child_id}/2026/planned",
+            json={"planned_days": 8},
+        )
+        assert put_planned.status_code == 200
+        body = put_planned.json()
+        assert body["is_default"] is False
+        assert body["planned_days"] == 8
+        assert body["taken_days"] is None
+
+        put_taken = await authed_client.put(
+            f"/api/preschool-planning-days/{seeded_ids.child_id}/2026/taken",
+            json={"taken_days": 5},
+        )
+        assert put_taken.status_code == 200
+        taken_body = put_taken.json()
+        assert taken_body["id"] == body["id"]
+        assert taken_body["planned_days"] == 8  # preserved
+        assert taken_body["taken_days"] == 5
+
+    async def test_record_taken_zero_distinguishable_from_default_none(
+        self, authed_client: AsyncClient, seeded_ids: SeededIds
+    ) -> None:
+        resp = await authed_client.put(
+            f"/api/preschool-planning-days/{seeded_ids.child_id}/2026/taken",
+            json={"taken_days": 0},
+        )
+        assert resp.status_code == 200
+        assert resp.json()["taken_days"] == 0
+        assert resp.json()["is_default"] is False
+
+    async def test_list_years_for_child(
+        self, authed_client: AsyncClient, seeded_ids: SeededIds
+    ) -> None:
+        await authed_client.put(
+            f"/api/preschool-planning-days/{seeded_ids.child_id}/2025/planned",
+            json={"planned_days": 6},
+        )
+        await authed_client.put(
+            f"/api/preschool-planning-days/{seeded_ids.child_id}/2026/planned",
+            json={"planned_days": 7},
+        )
+
+        resp = await authed_client.get(f"/api/preschool-planning-days/{seeded_ids.child_id}")
+        assert resp.status_code == 200
+        years = [row["year"] for row in resp.json()]
+        assert years == [2026, 2025]
+
+    async def test_unknown_child_returns_404(self, authed_client: AsyncClient) -> None:
+        resp = await authed_client.get(f"/api/preschool-planning-days/{uuid4()}/2026")
+        assert resp.status_code == 404
+
+    async def test_rejects_negative_planned_days(
+        self, authed_client: AsyncClient, seeded_ids: SeededIds
+    ) -> None:
+        resp = await authed_client.put(
+            f"/api/preschool-planning-days/{seeded_ids.child_id}/2026/planned",
+            json={"planned_days": -1},
+        )
+        assert resp.status_code == 422